The candidate is an Instructor in Anesthesiology at Brigham and Women's Hospital, Boston, MA. He will use the next 5 years to acquire basic molecular biology and electrophysiology skills to achieve his long-term goal of developing clinically useful pharmacological agents for the safe and specific treatment of pain. Local anesthetics (LAs) are used routinely for surgical anesthesia and for management of acute and chronic pain from all causes. In addition to blocking voltage-gated Na+ channels in sensory nerves fibers, LAs also block Na+ channels in motor and sympathetic fibers, as well as in brain and heart. Therefore, complete pain relief often cannot be accomplished, or serious adverse effects occur, e.g., cardiac arrest, seizures, low blood pressure, and motor blockade causing immobility. The specific aims of this proposal are (1) To identify novel drugs with LA properties in vivo and in vitro. (2) To examine these drugs for pain-selective properties. (3) To define their affinities to both the activated and inactivated states of different Na+ channel isoforms and (4) Using site directed mutagenesis, map the LA receptor in sensory neuron-specific Na+ channels to aid in future drug design. Whole-cell voltage-clamp recordings of newly developed quaternary ammonium (QA) derivatives of lidocaine (tonicaine) and amitriptyline (e.g., N-methyl amitriptyline) defined a high level of additional block (use-dependent block) when neuronal cells were stimulated at a high frequency. These QA drugs will be used to study the hypothesis that they selectively treat conditions caused by high-frequency discharge, e.g., acute postoperative and neuropathic pain. To further improve design of new drugs, the candidate will use drugs with good clinical properties (best efficacy and the fewest side effects in treating postoperative and neuropathic pain in animal surgical models) to define their binding sites in sensory neuron-specific Na+ channels transiently expressed in mammalian cells. It is hypothesized that this binding site is in areas responsible for use-dependent blockade, as there is no difference of the intrinsic affinity among different Na+ channel isoforms. With the use of site-directed mutagenesis, detailed structural information about the LA binding site in sensory-specific Na+ channels will be obtained by studying the effects of specific amino acid mutations on LA action and will help to direct and further refine drug design efforts.